Controlling a Non-Linear Space Robot using Linear Controllers

Space robots have been under intensive consideration to perform various in-orbit operations like the servicing of satellites, assembly of large structures, maintenance of other space assets and debris removal.Such orbital missions require a servicer spacecraft equipped with one or more dexterous manipulators.However, unlike its terrestrial counterparts, the base of the robotic manipulator is not fixed in inertial space.Additionally, the system will be subjected to extreme space environmental perturbations, parametric uncertainties as well as system constraints due to the dynamic coupling between the manipulator and the base-spacecraft.This paper presents the dynamic model of the space robot and a three-stage control algorithm to control such a highly non-linear system.In this approach, Feed-Forward compensation and Feed-Forward Linearization techniques are used to decouple and linearize the system, therefore allowing the testing of the linear PID and LQR controllers as final stages.Moreover, a simulation-based trade-off analysis was conducted to assess the efficacy of the proposed controllers.This assessment considered the requirements on precise trajectory tracking, minimizing power consumption and robustness during the close-range operation with the target spacecraft.